Measuring Wind Speed in Knots

In meteorology (and in sea and air navigation as well), a  knot is a unit of speed  typically used to indicate  wind speed. Mathematically, one knot is equal to about 1.15 statute miles. The abbreviation for a knot is kt or kts if plural. Why Knot Miles per Hour?   As a general rule in the US, wind speeds over land are expressed in miles per hour, while those over water are expressed in knots (largely because knots were invented over a water surface).  Since meteorologists deal with winds over both surfaces, they adopted knots for the  for the sake of consistency. However, when passing along wind information to public forecasts, knots are typically converted into miles per hour for the publics ease of understanding.    Why Is Speed at Sea Measured in Knots? The reason why sea winds are measured in knots at all has to do with maritime  tradition.  In centuries past, sailors didnt have GPS or even speedometers to know how fast they were traveling across the open sea. So to estimate their vessels speed,  they crafted  a tool made up of a  rope several  nautical miles in length with knots tied at intervals along it and a piece of wood tied at one end. As the ship sailed along, the wood  end of the rope was dropped  into the ocean and remained roughly in place as the ship sailed away. The number of knots was counted as they  slipped off of the ship  out to sea over  30 seconds (timed using a glass timer). By counting the number of knots that unspooled within that 30-second period, the ships speed could be estimated.   This not only tells us where the term knot comes from but also how the knot relates to a nautical mile: it turned out that the distance between each rope knot equaled one nautical mile. (This is why 1  knot is equal to 1 nautical mile per hour, today.)   Unit of Measure Surface winds mph Tornadoes mph Hurricanes kts (mph in public forecasts) Station Plots (on weather maps) kts Marine forecasts kts Units of Wind for Various Weather Events & Forecast Products Converting Knots to MPH Because being able to convert knots to miles per hour (and vice versa) is a must. When converting between the two, keep in mind that a knot will look like a lower numerical wind speed  than a mile per hour.  (One trick to remembering this is to think of the letter m in miles per hour as standing for more.) Formula to convert knots to mph:#  kts * 1.15   miles per hour Formula to convert mph to knots:#  mph * 0.87   knots Since the SI unit of speed happens to be  meters per second (m/s), it might also be helpful to know  how to convert wind speeds to these units. Formula to convert knots  to m/s:#  kts  * 0.51   meters per second Formula to convert mph to m/s:#  mph * 0.45   meters per second If you dont feel like completing the math for the conversion of knots to miles per hour (mph) or kilometers per hour (kph), you can always use a free online wind speed calculator to convert the results.